Field of the Invention
The present invention relates to a high-frequency discharge ignition device which ignites an internal combustion engine by supplying a high-frequency AC current to a spark discharge path and forming discharge plasma in a gap between electrodes of an ignition plug.
Background Art
In recent years, the problems of environmental conservation and fuel depletion have been raised, and in the automobile industry, there is a pressing need to respond to these problems. As an example of the response, a method which remarkably improves the amount of fuel consumption by engine downsizing and reduction in weight using a supercharger is known.
It is known that if a highly supercharged state is reached, the pressure in an engine combustion chamber becomes extremely high in a state not accompanied by combustion, and in this situation, it is difficult to generate spark discharge for starting combustion. One of the reasons is that a required voltage for causing dielectric breakdown between a high-voltage electrode and a GND (ground) electrode of the ignition plug becomes extremely high and exceeds a withstand voltage value of an insulator of the ignition plug.
In order to solve this problem, although studies have been done to increase the withstand voltage of the insulator, it is practically difficult to secure a sufficient withstand voltage as required, and means for narrowing the gap interval of the ignition plug should be provided. However, if the gap of the ignition plug is narrowed, there is a problem in that there is an increasing influence of a flame-out action by the electrode portion, causing degradation of startability and degradation of combustibility.
In order to solve this problem, avoidance means for providing energy greater than heat taken to the electrode portion by the flame-out action using spark discharge or for causing combustion in a part even slightly away from the electrodes is considered. For example, an ignition coil device described in Patent Document 1 has been suggested.
The ignition coil device disclosed in Patent Document generates spark discharge in a gap of an ignition plug by an ignition coil of the related art and supplies a high-frequency AC current to a spark discharge path through a mixer, making it possible to form spark discharge with high energy and discharge plasma spreading in a wider range than normal spark discharge.
[Patent Document 1] Japanese Patent No. 5351874
[Patent Document 2] JP-A-2013-177881
Since the ignition coil device of the related art described in Patent Document 1 supplies the AC current to the spark discharge path, the spark discharge path should be formed.
However, discharge plasma by an excessive AC current promotes electrode wear of the ignition plug, and if the electrodes are worn, the spark discharge gap is widened. When this happens, the discharge voltage of the ignition plug becomes high and exceeds the insulation withstand voltage of the ignition plug, and dielectric breakdown may occur in the ignition plug.
If the discharge voltage of the ignition plug exceeds the high voltage generated by the ignition coil, it is not possible to form the spark discharge path in the ignition plug. For this reason, it is necessary to grasp the discharge voltage of the ignition plug to grasp the discharge state of the ignition plug and the deterioration state of the ignition plug.
According to Patent Document 2, while it is possible to grasp deterioration of the ignition plug to some extent and to find out that the discharge voltage of the ignition plug becomes high, it is not possible to find out that the discharge voltage becomes abnormally low. A special element, such as a Zener diode of a high voltage, is required, and since the element is connected to the secondary coil of a high voltage, an element capable of withstanding a high voltage is required or insulation processing is required, causing a problem in terms of cost.